The present invention relates to gas-flow units which are adapted to be mounted on gas-administration apparatus and in particular, to gas-flow units such as vaporisers which are adapted to be mounted on apparatus for the administration of gaseous anaesthetics or analgesics (which, for convenience, will hereinafter be referred to collectively as "anaesthetics") or other "medical" gases or gas mixtures such as oxygen or air.
For the purposes of this specification the term "gas-flow unit" is intended to embrace any type of unit which is mountable on a gas-administration apparatus and adapted to receive a gas supply during the operation of the apparatus "Gas-flow units" therefore comprise, inter alia vaporisers, flow meters, gas mixers, volume meters, ventilators, pressure gauges and absorbers.
In United Kingdom patent specification No. 1,385,670 there is described a gas-administration apparatus on which one or more gas-flow units can be mounted in a removable, plug-in fashion. A plug-in system of this nature simplifies the installation and removal of gas-flow units from the apparatus, so facilitating maintenance and cleaning of the units, as also the replacement of a unit should it fail during an operation. Furthermore, this system is of great value to the anaesthetist in allowing him to change the unit(s), for example, vaporiser(s) installed on a given anaesthesia apparatus both easily and quickly. In this way the apparatus can readily be adapted for the administration of any one (or more) of the wide range of volatile anaesthetic agents currently available and the anaesthetist can accordingly ensure that the correct agent is made available for the needs of every patient.
Known gas-flow units adapted for the aforesaid `plug-in` type of system usually include a locking mechanism or member which cooperates with a backbar or rack of the anaesthesia apparatus to physically lock the unit in place when installed. Operation of the lock may also be effective to pull the unit tightly against seals provided around the cooperating ports which are provided on the anaesthesia apparatus to effect the desired gas supply to the unit. However, it is possible to install a known unit of this type and thereafter operate the apparatus without the lock having been moved into its operative position. The installed but unlocked gas-flow unit may thereby be inadvertently displaced or in any event gas leakage may occur past the seals which have not been compressed by operation of the lock and which are therefore not fully effective.